Why do computer games fascinate people? Because you get a feedback ever time you do something in a game. If your pac-man eats some dots or a ghost you get at once your points to bigger your high score. In a crpg like PoE it would be a lot of other things (e.g. exploring the wilderness, talking to NPCS in the way I like it as a character, accomplish tasks, etc.) that motivates me to play on and on. XP for slaying monsters is the most classic one and therefore I would realy like to see it in this game. But there are so many motivating things to do - to play in this game, that give you a positive feedback - even to listen to the great music and ambient sounds that XP for slaying monsters can even be on a very low place on the scale of importance. PoE is going a new way in terms of character attributes, so why not try to gain XP in a "new" (other) way than slaying monsters or picking locks.